The present invention relates to a projector in which light beams of respective colors that are modulated by liquid crystal light valves are synthesized by a dichroic prism, and the light beams are enlarged and projected onto a screen via a projection lens.
Color synthesizing devices used in conventional projectors include dichroic prisms. Ordinarily, in a dichroic prism, four right-angled triangular prisms are pasted to each other in an X-shaped pattern with the right angles of these prisms contacting each other, and reflective films, such as conductive films or the like, that have selective reflectivity for specified colors, are formed on the pasted faces (it will be assumed herein that such reflective films are formed unless otherwise noted).
Currently, glass is the main material used for such right-angled triangular prisms; however, in recent years, prisms formed by injection or compression molding of plastics have begun to be used, as described in Japanese Patent Application Laid-Open No. 2001-66694.
A method used to manufacture such a dichroic prism will be described with reference to FIG. 3.
First, a first triangular prism 19 and a second triangular prism 20 are pasted together on the same plane using the planes 19a and 20a (among the planes on either side of the right angles of the prisms) as reference planes. Then, a third triangular prism 21 and a fourth triangular prism 22 are similarly pasted together.
Next, the unit formed by the first triangular prism and second triangular prism is pasted to the unit formed by with the third triangular prism and fourth triangular prism. However, in this case, since there is no reference plane, it is difficult to align the positions of the vertex parts in each unit so that the prisms are accurately pasted together. As a result, if a positional deviation xcex4 occurs do to inaccurate alignment of the pasted faces (as shown, for example, in FIG. 3), the images of respective colors that are synthesized via the dichroic prism thus obtained will not be aligned on the screen, so that the image quality drops.
A method for accurately pasting the units together to align the vertex positions of the respective prisms in order to eliminate such a drop in the image quality is described in Japanese Patent Application Laid-Open No. 8-184793. In this method, as shown in FIG. 4, a pair of prisms 23 and 24 (among four prisms 23, 24, 25 and 26) are first pasted together so that a step is formed between the two prisms. Furthermore, the remaining pair of prisms 25 and 26 are also similarly pasted together so that a step is formed between the two prisms. Finally, the respective pairs of prisms are pasted together using these step faces 23a and 25a to guide the positioning of the faces so that the vertex parts are in alignment.
In cases where right-angled triangular prisms made of glass are used, the manufacture thereof includes a polishing process. Accordingly, faces that are perpendicular to the faces through which the light beams pass can easily be formed to have a perpendicular orientation. Consequently, even in the case of conventional techniques, dichroic prisms can be formed with a high degree of precision.
However, in the case of the abovementioned right-angled triangular prisms formed by injection or compression molding of plastics, an inclination of substantially 2 to 5 degrees is generated in connection with the injection from the mold.
If an attempt is made to form a dichroic prism by the method described in Japanese Patent Application Laid-Open No. 8-184793, using right-angled triangular prisms that have such an inclination, the faces that have steps can be aligned, but the directions perpendicular to these faces cannot be aligned.
Accordingly, since the edge lines of the right angles of the four prisms that are pasted together cannot be accurately pasted, the light beams of the respective colors cannot be synthesized with a high precision for each pixel, so that desired colors cannot be reproduced. Furthermore, the edge lines themselves will be projected and displayed as vertical stripes on the image.
It is an object of the present invention to improve the precision of color synthesis, and to suppress vertical stripes in a projected image.
In order to achieve the abovementioned object, the present invention includes the following aspects:
(1) A projector comprising a light source, color separating means for separating the light beam emitted from this light source into light beams of respective colors, light valves which modulate the separated light beams of respective colors, a dichroic prism which synthesizes the modulated light beams of respective colors that have been modulated via the light valves, and a projection lens which enlarges and projects the synthesized modulated light beam onto a screen, wherein the dichroic prism is a prism formed by pasting together four triangular prisms, which are substantially right-angled triangular prisms as seen in cross section, and triangular prisms in which projections or grooves that have two faces forming planes parallel to the two pasted faces are integrally molded in the faces that are substantially perpendicular to the light beams (i.e., faces through which the light beams do not pass) are used as the abovementioned triangular prisms.
(2) A projector comprising a light source, color separating means for separating the light beam emitted from this light source into light beams of respective colors, light valves which modulate the separated light beams of respective colors, a dichroic prism which synthesizes the modulated light beams of respective colors that have been modulated via the light valves, and a projection lens which enlarges and projects the synthesized modulated light beam onto a screen, wherein the dichroic prism is a prism formed by pasting together four triangular prisms, which are substantially right-angled triangular prisms as seen in cross section, and triangular prisms in which marks used for positioning are formed on the pasted faces are used as the abovementioned triangular prisms.
(3) A projector comprising a light source, color separating means for separating the light beam emitted from this light source into light beams of respective colors, light valves which modulate the separated light beams of respective colors, a dichroic prism which synthesizes the modulated light beams of respective colors that have been modulated via the light valves, and a projection lens which enlarges and projects the synthesized modulated light beam onto a screen, wherein the dichroic prism is a prism formed by pasting together four triangular prisms, which are substantially right-angled triangular prisms as seen in cross section, and these triangular prisms are engaged with each other by means of projections or grooves formed in the pasted faces.